The retinoid-related orphan receptors, RORα, RORβ, and RORγ, play an important role in numerous biological processes including organ development, immunity, metabolism, and circadian rhythms. See, for example, Dussault et al. in Mech. Dev. (1998) vol. 70, 147-153; Andre et al. in EMBO J. (1998) vol. 17, 3867-3877; Sun et al. in Science (2000) vol. 288, 2369-2373; and Jetten in Nucl. Recept. Signal. (2009) vol. 7, 1-32.
RORγ is expressed in several tissues including the thymus, kidney, liver, and muscle. Two isoforms of RORγ have been identified: RORγ1 and RORγ2 (also known, respectively, as RORγ and RORγt). See, for example, Hirose et al. in Biochem. Biophys. Res. Commun. (1994) vol. 205, 1976-1983; Oritz et al. in Mol. Endocrinol. (1995) vol. 9, 1679-1691; and He et al. in Immunity (1998) vol. 9, 797-806. Expression of RORγt is restricted to lymphoid cell types including CD4+CD8+ thymocytes, IL-17 producing T helper (Th17) cells, lymphoid tissue inducer (LTi) cells, and γδ cells. RORγt is essential for the development of lymph nodes and Peyer's patches and for the normal differentiation of Th17, γδ, and LTi cells. See, for example, Sun et al. in Science (2000) vol. 288, 2369-2373; Ivanov et al. in Cell (2006) vol. 126, 1121-1133; Eberl et al. in Nat. Immunol. (2004) vol. 5, 64-73; Ivanov et al. in Semin. Immunol. (2007) vol. 19, 409-417; and Cua and Tato in Nat. Rev. Immunol. (2010) vol. 10, 479-489.
Proinflammatory cytokines such as IL-17A (also referred to as IL-17), IL-17F, and IL-22 produced by Th17 cells and other RORγ+ lymphocytes activate and direct the immune response to extracellular pathogens. See, for example, Ivanov et al. in Semin. Immunol. (2007) vol. 19: 409-417; and Marks and Craft in Semin. Immunol. (2009) vol. 21, 164-171. RORγ directly regulates IL-17 transcription and disruption of RORγ in mice attenuates IL-17 production. See, for example, Ivanov et al. in Cell (2006) vol. 126, 1121-1133.
Dysregulated production of IL-17 has been implicated in several human autoimmune and inflammatory diseases including multiple sclerosis, rheumatoid arthritis, psoriasis, inflammatory bowel disease (IBD), and asthma. See, for example, Lock et al. in Nat. Med. (2002) vol. 8, 500-508; Tzartos et al. in Am. J. Pathol. (2008) vol. 172, 146-155; Kotake et al. in J. Clin. Invest. (1999) vol. 103, 1345-1352; Kirkham et al. in Arthritis Rheum. (2006) vol. 54, 1122-1131; Lowes et al. in J. Invest. Dermatol. (2008) vol. 128, 1207-1211; Leonardi et al. in N. Engl. J. Med. (2012) vol. 366, 1190-1199; Fujino et al. in Gut (2003) vol. 52, 65-70; Seiderer et al. in Inflamm. Bowel Dis. (2008) vol. 14, 437-445; Wong et al. in Clin. Exp. Immunol. (2001) vol. 125, 177-183; and Agache et al. in Respir. Med. (2010) 104: 1131-1137. In murine models of these diseases, inhibition of IL-17 function by neutralizing antibodies or genetic disruption of IL-17 or IL-17 receptor ameliorates the disease course or clinical symptoms. See, for example, Hu et al. in Ann. N.Y. Acad. Sci. (2011) vol. 1217, 60-76.
Disruption of RORγ in mice also attenuates disease progression or severity in animal models of autoimmunity and inflammation including experimental autoimmune encephalomyelitis (EAE), imiquimod induced psoriasis, colitis, and allergic airway disease. See, for example, Ivanov et al. in Cell (2006) vol. 126, 1121-1133; Yang et al. in Immunity (2008) vol. 28, 29-39; Pantelyushin et al. in J. Clin. Invest. (2012) vol. 122, 2252-2256; Leppkes et al. in Gastroenterology (2009) vol. 136, 257-267; and Tilley et al. in J. Immunol. (2007) vol. 178, 3208-3218.
Each of the references in this Background section is hereby incorporated herein by reference in its entirety for all purposes.
Therapeutic agents exist to treat a variety of inflammatory and autoimmune diseases, but there still remains a significant unmet medical need in these therapeutic areas. Given the role of IL-17 in human disease and the validation of IL-17 and RORγ as targets in murine disease models, compounds capable of modulating RORγt activity are contemplated to provide a therapeutic benefit in the treatment of multiple immune and inflammatory disorders.